**6. Final remarks**

process and (2) the lignin and solid residuals are used for energy production. This can be achieved by adopting a biorefinery concept in which several process technologies are combined to convert biomass into multiple products [28]. A simplified diagram of an integrated

**Table 3** shows the energy ratios reported for several integrated bioethanol processes in biorefineries. It can be observed that an energy ratio of up to 0.5 can be achieved using a simultaneous saccharification and fermentation process, including strategies (1) and (2) aforementioned. Energy integration using pinch analysis is also essential to reduce process utility

It is important to examine the life cycle emissions as the bioethanol process uses additional inputs, including enzymes, nutrients, salts, neutralizers, and so on. An average value of 6.2 kg

Comparing the two options for bagasse utilization, a study shows that the use of bagasse for power generation results in lower global warming, acidification and eutrophication potentials, whereas the bioethanol production provides resource conservation (by replacing fossil fuel) and lower human- and eco-toxicity [33]. In terms of energy balance, with the use of advanced technologies and process integration, both systems are able to achieve high efficiency level up to 50% in the bioethanol case. Up to 65% of the energy from bagasse incineration can be recovered by the biorefinery system in **Figure 3**, while only 32–33% of the energy is recovered by stand-alone bioethanol production [39]. Therefore, the use of multistage steam condensing turbines, efficient boilers, as well as the integrated first-generation + second-generation system with energy recovery from solid residues and biogas from wastewater treatment is highly recommendable to achieve high efficiency levels and environmental benefits from sugarcane

/kg ethanol has been reported [35]. More comprehensive results of life cycle assessment environmental impacts are shown in **Table 4** for the impact categories of global warming potential (GWP-100 years), abiotic resource depletion (fossil fuels), eutrophication and acidification potentials of the integrated biorefinery system in **Figure 3**. These results show that the amount of GWP can be negative due to the savings by replacing fossil fuels by ethanol and

biorefinery system is shown in **Figure 3**.

78 Sugarcane - Technology and Research

bagasse and sugarcane as an energy crop.

CO<sup>2</sup>

requirements and increase energy efficiency [35, 37].

grid electricity by the power generated from lignin and biogas.

**Figure 3.** Integrated system for bioethanol production from sugarcane bagasse.

Sugarcane mills are one of the major industrial facilities in tropical and developing countries, generating income and jobs in the rural agricultural sector. These important industrial systems are evolving from single product process producing sugar to sweeten drinks and food, to sugar and bioenergy generation in the form of electricity and also biofuels. The valorization of sugarcane bagasse as a resource for energy and bioethanol production has been reviewed in this chapter from the perspective of energy ratio and emissions. Trade-offs between the two bagasse applications have been found with incineration for power generation being favorable toward reducing potential impacts of global warming while bioethanol being more favorable toward resource conservation and lower toxicity. Advanced integrated biorefineries can achieve energy ratios similar to those in incineration for power-only systems, especially if second-generation bioethanol production from cellulose and hemicellulose and electricity from lignin are combined in the sugar mill facilities. Sugarcane mills have the potential to be retrofitted and converted into advanced biorefineries being energy self-sufficient and co-producing other value-added products from sugarcane bagasse in a wide range of applications such as energy, biochemicals, food and feed and materials sectors. Comprehensive energetic, economic and environmental assessment of the various alternative uses and process technologies need to be carried out considering the various efficiencies of the value chain, from cultivation to processing and end use, in order to find the best alternative in a given socioeconomic context.

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